This invention relates generally to electronics and more particularly to the problem of reducing electromagnetic interference (EMI) signal radiation in cables.
A computer system, such as a personal computer or notebook computer, emits EMI radiation and other electronic xe2x80x9cnoisexe2x80x9d due to the electronic components included in the computer system. Various threshold values defining acceptable levels of EMI radiation from a computer system have been established, for example, by governmental agencies. To be EMI-compliant in accordance with these established EMI radiation limits, computer manufacturers have taken steps to minimize EMI radiation levels emitted from various components of computer systems. For example, a special metallic casing may be used over a liquid crystal display (LCD) device, or a special metallic paint may be used on the inside of computer casings to minimize EMI emissions. EMI radiation is also emitted from wires and cables used in a computer system to interconnect various components, such as to connect a display device to the motherboard. Various techniques are used to reduce EMI emissions from the cables. However, special considerations must be taken when reducing the EMI radiation of the cables included in the smaller notebook computer systems.
Physical constraints exist when considering the smaller computer systems being developed today, such as the thin notebooks and laptop computers, that are not typically constraints in the conventional personal computer system. For example, when electrically connecting, with a cable, a component in the top portion of the notebook to another component in the bottom portion, an additional constraint is the constant, sharp, bending which occurs at the crease where the top and bottom meet as the notebook is opened and closed. This is not a constraint in a conventional personal computer system having a separate monitor and processor. An additional constraint in the smaller notebook computer systems is the smaller amount of space, for example, of openings through which cables pass, and for housing the components. In other words, due to the density of the overall packaging of the computer system components in a notebook computer, there is little free space, for example, for cable routing. The relevance of these additional constraints, which must be considered when attempting to reduce EMI emissions in the cables used in notebook computer systems, is described in paragraphs below.
One type of cable typically used in computer systems is xe2x80x9cflexprintxe2x80x9d cable used to connect, for example, a transmitter on the motherboard to a receiver included in the LCD device. The transmitter is located in the bottom portion of the notebook computer and the receiver is located in the top portion of the notebook computer. Generally, a flexprint cable includes multiple signal conductors surrounded by flexible layers of insulating tape, such as a mylar tape. One drawback with using the flexprint cable in the small, thin, notebook computers when connecting a component in the top portion to another component in the bottom portion is that the flexprint cable is often not flexible enough. Constant bending of the flexprint cable within the casing at the crease where the top and bottom of the notebook meet, as when the notebook is opened and closed, typically causes cable conductors in the flexprint cable to fracture over time. Another drawback is that EMI radiation levels are often not reduced enough with the flexprint cable at the high data transfer rates, for example, above 650 megabits/second, and increased frequencies with newer display devices, such as an xe2x80x98XGAxe2x80x99 or xe2x80x98SXGAxe2x80x99 display device. Examples of the increased frequencies in this range typically include a fundamental operating frequency at or above 65 MHZ with harmonics in the 10xc3x97 range of 650 MHZ. Typically, an xe2x80x98XGAxe2x80x99 device has a resolution of 1024 by 768 pixels, and an xe2x80x98XSGAxe2x80x99 device has a resolution of 1280 by 1024 pixels.
Another type of cable typically used in computer systems to electrically connect components is a shielded cable or wire, such as copper. These types of cables using shielded wire include a point-to-point wire connection, a twisted wire pair, or a standard coaxial cable. Typically, the point-to-point and twisted wire pair are in the general size range of 22-30American Wire Gauge (AWG), and the coaxial cable is generally greater than 20 AWG . One drawback with using wires of this type is that they are often too large to be used in small notebook computer systems given the previously described density and housing of computer components. Wires of this type may be too large in notebook computers in two respects. First, when electrically connecting two components having a high data transfer rate, the number of interconnecting wires required for the electrical connection often exceeds the size of the opening. For example, when electrically connecting for data s transfer the data receiver of the LCD, located in the top portion of the notebook, to the transmitter on the motherboard in the bottom portion of the notebook, the cumulative size of all the wires required to transmit the necessary data often exceeds the narrow openings allowed for the connection. Secondly, even if the total number of interconnecting wires is reduced, the existing wires plus necessary shielding still often render the wires too large for use in a notebook computer.
Still another drawback using shielded wires, as with the flexprint cable, is that EMI radiation levels are not sufficiently reduced with some wire cable configurations when using the high data transfer rates and increased frequencies.
Thus, there is required an efficient technique for providing electrical connections between computer components which minimizes EMI radiation emissions, has a high degree of physical flexibility, and requires a minimum amount of space.
In accordance with principles of the present invention, a cable bundle used in a notebook computer is disclosed. The cable bundle is used for data transmissions between a transmitter in the bottom portion of the notebook computer, and a receiver in the top portion of the notebook computer. The cable bundle includes multiple coaxial cables each transmitting an electrical signal, and one or more outer cable layers surrounding the coaxial cables. Each of the coaxial cables in the cable bundle further includes an inner conductor portion, a dielectric medium surrounding the inner conductor portion, and a twisted served shield helically wrapped around the dielectric medium.
In accordance with another aspect of the invention, disclosed is a cable bundle used in data transmissions in which the cable bundle includes multiple cables each transmitting an electrical signal, and a layer of neoprene rubber tubing. The layer of neoprene rubber tubing also includes particles with magnetic properties suspended in a rubber binder material.
Thus, there is provided an efficient technique for providing electrical connections between computer components which minimizes EMI radiation emissions, has a high degree of flexibility, and requires a minimum amount of space.